Thermal switch



y 1949' c. M. OSTERHELD 2,475,292

THERMAL SWITCH Filed Jan. 4, 1947 INVENTOR.

CLARK M. OSTERHELD Patented July 5, 1949 THERMAL SWITCH Clark M. Osterheld, Stouhton, Wis., assignor to McGraw Electric Company, Elgin poratlon of Delaware Application January 4, 1947, Serial No. 720,163

My invention relates to thermal switches and particularly to snap-acting thermal switches.

An object of my invention is to provide a novel form of snap-acting thermal switch.

Another object of my invention is to provide a snap-acting thermal switch that shall be of relatively small temperature differentia1 operation.

Still another object of my invention is to provide a relatively simple and strong construction that shall be effective to operate over a relatively long period of time,

Other objects of my invention will either be obvious from a description of several modifications of device embodying my invention or will be pointed out in the course of such description and be set forth particularly in the appended claims.

In the drawings,

Figure 1 is a top-plan view of a snap-acting thermal switch embodying my invention,

Fig. 2 is a view in longitudinal section taken on the line 2-4 of Fig. 1,,

Fig. 3 is an end view 3-3 of Fig. 1,

Fig. 4 is a vertical lateral section therethrough taken on the line 5-4 of Fig. l, and,

Fig. 5 is a fragmentary top-plan view of a modified form of device embodying my invention.

A snap-acting thermal switch H includes a skeleton frame of cast aluminum or other metal comprising a longitudinally extending bar it, a second longitudinally extending bar I5 having a recess therein at one side thereof and two lateral bars i9 and 2! respectively.

Upon bar i9 I mount a relatively thin metallic bar 25 which in Fig. 1 of the drawings is pivotally supported on bar it by a central screw 27. The construction of bar 25 and its mounting upon a screw 21 is such that bar 25 may move easily and freely on screw 21.

I provide a bimetal bar 29 which has a loose pivotal mounting upon a pin 3|, which pin 3! is fixedly mounted upon one end of bar 25. The other end of bimetal bar 29 is pivotally mounted on a screw 23 which is fixedly mounted on bar it.

I provide a preshaped snap-acting single metal spring bar 33 having one end thereof secured loosely around screw 23, while its other end is mounted on a pin 35 which is secured to bar 25. The bimetal bar 29 is of arcuate shape and it the switch is to open in response to an increase in temperature, the high expansion component thereof taken on the line 7 Claims. (Cl. 200-439) b on the upper side of bimetal bar 29, as seen in Fig. 1 of the drawings. 1 have found that when the bimetal bar 28 is bent to arcuate shape, the radius of curvature being on the order or 4" or 5", that bimetal bar 29 will exert a relatively large pressure when subjected to increase in temperature, with the result that spring bar 33 will-move downwardly with a snap action when a predetermined higher temperature has been reached.

I provide a, contact bridging member 31 on bar 33, whichcontact bridging member is supported by bar'33 through a bar 39 of electric insulating material secured to bar 33. I provide a pair of contact members 4| and 43 mounted on a small plate 45 of electric-insulating material which is secured to bar l5. Each of the contact members it and 43 is provided with an externally screwthreaded part 41 so that a circuit wire may be fixedly connected with each 01? the members 41.

Referring now to Fig. 5 of the drawings, I have there shown a modified form of snap-acting thermal switch embodying my invention, the modification comprising particularly the provision of a pivotal mounting 101' bar 25 which is no longer at substantially the mid point of the length of bar 25 butis preferably so positioned that the distance of pivot pin 2? from pin 5| is less than the distance of pivot pin 2'! from pin 35. It will be evident that the differential of operation of bimetal bar 29 need be less to cause opening or disengagement or contacts ill and -43 from contact bridging member 31 than if the pivot pin 2! were at substantially the mid point of bar 25.

In order to permit of varying the temperature at which the switch will operate I may provide a'manually adjustable screw-threaded member 39, having screw-threaded engagement with bar l3, turning of bar 49 in one direction or the other causing a change of the initial setting of bimetal bar 29 and therefore causing a change of temperature at which operation of the switch as described above will occur.

Various modifications may be made in the device embodying my invention without departing from the spirit and scope thereof and I desire that all such modifications coming-clearly within the scope of the appended claims shall be considered a part of my invention.

I claim as my invention:

1. A snap-actingthermal switch comprising a preshaped spring bar, a contact normally engag ing said bar, a. fixedly mounted pin pivotally supporting one end of said bar, a bimetal bar will 5 preslmped to bowed form having one end pivotally supported, a short lever arm pivotally supported intermediate its endsv and having the other ends of said spring bar and said bimetal bar pivotally connected to its ends, snap-acting movement of said spring bar away from said contact being effected by increase in the overall length 01 said bimetal bar upon change of its temperature.

2. A snap-acting thermal switch comprising a preshaped spring bar, a contact normally engaging said bar, a fixedly mounted pin pivotally supporting one end of said bar, a bimetal bar preahaped to bowed form having one end pivotally supported, and a short lever arm fixedly pivotally mounted so that its Divot pin divides the arm into unequal lengths and having its ends pivotally connected to the other end of said spring bar and said bimetal bar, snap-acting disengagement oi! said spring bar and said contact being effected upon'change of distance between the ends of said bimetal bar upon change of its temperature.

3. A snap-acting thermal switch comprising a preshaped spring bar, a contact normally engaging said bar, a fixedly mounted'pin pivotally supporting one end of said bar, a bimetal bar preshaped to bowed form having one end pivotally supported, a relatively short lever arm, a fixedly mounted pivot pin secured to said lever arm intermediate the ends thereof and so as to divide the lever arm into a short and a long length, the other end of said bowed bimetal bar being pivotally secured to the lever arm at the short end, the other end of said spring bar being pivotally secured to the'other end of said lever arm, snap-acting disengagement of said spring bar and said contact being effected by increase in distance between the ends of said bimetal bar upon increase in temperature thereof.

4. A thermal switch as set forth in claim 1 and including manually-actuable means engaging 4 said bimetal bar for changing the temperature at which said snap-acting movement of the spring bar takes place.

5. In combination in a snap-acting thermal control device, a long thin springgstrut, a long thin strut o! resilient, thermally-responsive blmetal that tends to alter its longitudinal curvature in response to changes of its temperature, a connection between an end of one strut and an end of the other for connecting the two struts end to end in series, a member for restraining at least one of said strut ends against lateral motion, means for supporting the other ends oi said struts for bowing said struts in longitudinal compression against each other, and a memberto-be-operated mechanically connected to a part of said spring strut intermediate its ends so as to be moved by said spring strut as its curvature is altered in response to changes oi temperature of said bimetal strut.

6. The combination of the immediately preceding claim wherein both struts are supported in articulate connections, and wherein said spring strut has a longitudinal curvature in its unstressed condition.

7. The combination of the immediately preceding claim wherein said bimetal strut also has a longitudinal curvature in its unstressed condiion.

CLARK M. OS'I'ERHELD.

REFERENCES CITED The following reierenlces are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,731,903 Mottlav Oct. 15, 1929 1,784,450 Klahn Dec. 9, 1930 

